The invention described herein was made by employees of the United States Government and may be used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention is generally related to piezoelectric fiber composite strain actuators.
2. Description of the Related Art
Conventional piezoelectric fiber composite actuators are typically manufactured using a layer of extruded piezoelectric fibers encased in protective polymer matrix material. Interdigitated electrodes etched or deposited onto polymer film layers are placed on the top and bottom of the fibers to form a relatively thin actuator laminate. Protecting the fibers in a matrix polymer strengthens and protects the piezoelectric material. The resulting package is more flexible and conformable than actuators formed from monolithic piezoelectric wafers. These actuators can be easily embedded within or placed upon non-planar structures using conventional manufacturing techniques. In addition, the use of interdigitated electrode poling permits production of relatively large, directional in-plane actuation strains. The directional nature of this actuation is particularly useful for inducing shear (twisting) deformations in structures.
Unfortunately, the methods of manufacturing conventional piezoelectric fiber composites typically use relatively high cost, extruded, round piezoelectric fibers. Moreover, alternative methods of manufacture using square fibers, which are milled from lower cost monolithic piezoelectric wafers, have been unsuccessful due to the difficulty of aligning individual square fibers during actuator assembly without shifting and rolling. Rolled square fibers tend to expose sharp corners and edges which can sever the interdigitated electrode layers during the final process of actuator assembly. Both the round and square fiber approaches require individual handling of piezoelectric fibers during assembly, thereby resulting in relatively high manufacturing costs.
Another disadvantage of conventional piezoelectric fiber composite actuators is the requirement of relatively high operating voltages. High operating voltages are needed to produce electric fields which are sufficiently strong to propagate through the protective polymer material encasing the piezoelectric fibers. These electrode voltages are several times higher than those theoretically required to produce a given strain in the unprotected piezoelectric material. Additionally, round fibers have a low contact area with the electrode, thereby causing losses and decreased efficiency. To compensate for these losses, increased voltages are required. Conventional techniques for applying electrodes directly in contact with the piezoelectric fibers have thus far not been practical.
It is therefore an object of the present invention to provide an improved piezoelectric fiber composite strain actuator and a method for making same.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in one aspect, a method for fabricating a piezoelectric macro-fiber composite actuator. The first step comprises providing a structure comprising piezo-electric material which has a first side and a second side. First and second films are then adhesively bonded to the first and second sides, respectively, of the piezo-electric material. The first film has first and second conductive patterns formed thereon which are electrically isolated from one another and in electrical contact with the piezo-electric material. In one embodiment, the second film does not have any conductive patterns. The first and second conductive patterns of the first film each have a plurality of electrodes that cooperate to form a pattern of interdigitated electrodes. In another embodiment, the second film has a pair of conductive patterns similar to the conductive patterns of the first film.
In a related aspect, the present invention is directed to a piezoelectric macro-fiber composite actuator, comprising:
a structure consisting of piezo-electric material having a first side and a second side;
a first film bonded to the first side of the structure, the film further including first and second conductive patterns formed thereon, the first conductive pattern being electrically isolated from the second conductive pattern, both conductive patterns being in electrical contact with the piezo-electric material structure, the first and second conductive patterns each having a plurality of electrodes that cooperate to form a pattern of interdigitated electrodes; and
a second film bonded to the second side of the structure.
In a further aspect, the present invention is directed to a piezoelectric macro-fiber composite actuator, comprising:
a plurality of piezoelectric fibers in juxtaposition, each fiber having a first side and a second side, each pair of adjacent fibers being separated by a channel;
a first adhesive layer disposed over the first sides of the fibers and in the channel,
a first film bonded to the first sides of the fibers, the film further including first and second conductive patterns formed thereon, the first conductive pattern being electrically isolated from the second conductive pattern, both conductive patterns being in electrical contact with the piezo-electric material structure, the first and second conductive patterns each having a plurality of electrodes that cooperate to form a pattern of interdigitated electrodes;
a second adhesive layer disposed over the second sides of the fibers and into the channels; and
a second film bonded to the second sides of the fibers, the second film having a first conductive pattern and a second conductive pattern electrically isolated from the first conductive pattern of the second film, the first and second conductive patterns of the second film being in electrical contact with the fibers, the first and second conductive patterns of the second film each having a plurality of electrodes that cooperate to form a pattern of interdigitated electrodes.